Linked area parameter adjustment for spinal cord stimulation and associated systems and methods

ABSTRACT

Systems and methods for managing pain in a patient using an electrical waveform that link the modulation of a waveform parameter for different areas of a patient. One embodiment in a system for managing pain in a patient comprises an electric device configured to be implanted into the patient and including a plurality of electrodes having at least a first electrode associated with a first area of the patient and a second electrode associated with a second area of the patient. The system further includes an implantable device configured to be coupled to the electrode device and having a computer-operable medium programmed to change the waveform parameter applied to the first electrode and automatically set the waveform parameter applied to the second electrode based on a relationship between a first therapy range and a second therapy range of the waveform parameter.

TECHNICAL FIELD

The present technology is directed generally to spinal cord stimulationfor managing pain, and associated systems and methods related toadjusting the amplitude, duty cycle and/or other parameters of theelectrical waveform applied to the patient.

BACKGROUND

Neurological stimulators have been developed to treat pain, movementdisorders, functional disorders, spasticity, cancer, cardiac disorders,and various other medical conditions. Implantable neurologicalstimulation systems generally have an implantable pulse generator andone or more leads that deliver electrical pulses to neurological tissueor muscle tissue. For example, several neurological stimulation systemsfor spinal cord stimulation (SCS) have cylindrical leads that include alead body with a circular cross-sectional shape and one or moreconductive rings or bands spaced apart from each other at the distal endof the lead body. The conductive rings operate as individual electrodesand, in many cases, the SCS leads are implanted percutaneously through alarge needle inserted into the epidural space either with or without theassistance of a stylet.

Once implanted, the pulse generator applies electrical signals via theelectrodes to modify the function of the patient's nervous system, suchas altering the patient's responsiveness to sensory stimuli and/oraltering the patient's motor-circuit output. In pain treatment, theelectrical signals can generate sensations which mask or otherwise alterthe patient's sensation of pain. For example, in many cases patientsreport a tingling or paresthesia that is perceived as more pleasantand/or less uncomfortable than the underlying pain sensation. Althoughthis may be the case for many patients, many other patients may reportless beneficial effects and/or results. Accordingly, there remains aneed for improving the techniques and systems for addressing patientpain.

One particular challenge of implementing neurological stimulators tomanage pain is that multiple parts or regions of the patient's bodycontribute to the pain perceived by the patient, and the individualcontributions of the various regions vary over time. For example,patients generally experience different levels of back pain and/or lowerextremity pain because of exertion, stress, movement (e.g., walking,bending, twisting, etc.), position (e.g., standing, sitting, etc.), andother factors. Patients accordingly change the parameters of theelectrical waveform in some or all of the affected regions on an ongoingbasis to effectively manage the pain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partially schematic illustration of an implantable spinalcord stimulation system positioned at the spine to deliver therapeuticsignals in accordance with an embodiment of the present technology.

FIG. 1B is a partially schematic illustration of a lead having electrodecontacts that form elements of one or more therapy circuits associatedwith different areas of the patient that are modulated in accordancewith methods of the present technology.

FIG. 2 is a flow diagram illustrating a process for managing pain usinglinked area parameter modulation.

FIG. 3A is a flow diagram illustrating a routine for determining atherapy range of a waveform parameter associated with an area for use inthe technology.

FIG. 3B is a flow diagram illustrating another routine for determiningthe therapy range of a waveform parameter associated with an area foruse in the technology.

FIGS. 4 and 5 are schematic illustrations of waveforms showingimplementations of methods for linked area parameter modulation inaccordance with the technology.

FIG. 6 is a flow diagram illustrating a process for managing pain usinglinked area modulation in accordance with another embodiment of thetechnology.

FIG. 7 is a flow diagram illustration another process for managing painusing linked area parameter modulation in accordance with a differentembodiment of the technology.

DETAILED DESCRIPTION

The invention herein described can be implemented in numerous ways,including as a process, a method, a routine, a device, an apparatus, asystem, a composition of matter, an electrical waveform, a computerreadable or operable medium such as a computer readable storage mediumor a computer network wherein program instructions that are sent overoptical or electronic communication links. In this specification, theseimplementations, or any other form that the invention may take, may bereferred as present technology or invention.

The present technology is directed generally to spinal cord stimulation(SCS) systems and methods for managing pain in a patient using anelectrical waveform (e.g., electrical signals). Specific details ofcertain embodiments of the disclosure are described below with referenceto changing one or more parameters of the electrical waveform applied todifferent areas of the patient using a spinal cord stimulator. Thedisclosed systems and methods, however, may be used in the context ofother stimulators and/or other patient conditions. Accordingly, someembodiments of the technology can have configurations, components, orprocedures different than those described in this section, and otherembodiments may eliminate particular components or procedures describedbelow. A person of ordinary skill in the relevant art, therefore, willunderstand that the technology may have other embodiments withadditional elements and/or other embodiments without several of thefeatures shown and described below with reference to FIGS. 1A-7.

Overview

During the trial period and the course of the SCS therapy itself, thepatients typically change the parameters of the waveforms applied todifferent areas along the spinal cord to optimize the therapy. Forexample, if the patient experiences leg and/or back pain that variesover time, patient position, and other factors, the patient inputschange commands via a patient programmer that causes the pulse generatorto increase or decrease one or more parameters of the electricalwaveform. In most SCS systems, the amplitude is the parameter that canbe modulated by the patient. Current SCS systems and processes, however,use complex devices with multiple settings to change the amplitudeacross multiple areas. Conventional systems usually include a manualmode in which the patient experimentally determines a suitablecombination of areas and the amplitudes to apply to those areas. Becausepatients typically perform this on a trial-and-error basis, it is oftenonly marginally effective and time consuming. Conventional systems mayalso include a linked mode in which the amplitudes of the waveformapplied to one or more areas are tied together so that the patientmerely adjusts the amplitude. Conventional linked mode systems adjustthe amplitudes equally across each area, but this can be ineffectivebecause different areas typically have different maximum amplitudethresholds above which the patient experiences increased pain levels. Asa result, existing linked mode systems are limited because the amplitudecan only be adjusted to the extent that the stimulation does not exceedthe level of the area having the lowest maximum amplitude threshold.Certain aspects of the present technology simplify this process andenhance the ability to quickly change the amplitude or other waveformparameter across a plurality of areas.

In some embodiments, the present technology includes an electrode devicehaving a plurality of electrodes including at least a first electrodeassociated with a first area of the patient and a second electrodeassociated with a second area of the patient. The first area has a firsttherapy range for a waveform parameter, and the second area has a secondtherapy range for the waveform parameter. The electrode device may beconfigured to be implanted into a patient. The technology furtherincludes a power supply, a waveform generator configured to generate thewaveform and a computer readable medium operatively coupled to thewaveform generator. In some embodiments, the technology further includesan implantable device configured to be coupled to the electrode deviceand the implantable device includes the power supply, the waveformgenerator configured to generate the waveform, and the computer-operablemedium operatively coupled to the waveform generator.

The technology can include delivering an electrical waveform at a firstlevel of the waveform parameter to a first electrode located at thefirst area and at a second level of the waveform parameter to a secondelectrode at the second area. The technology can further includechanging the first level of the waveform parameter to an updated firstlevel, setting the second level of the waveform parameter based on thescaling factor to an updated second level, and delivering the electricalwaveform at the updated first level of the waveform parameter to thefirst electrode and at the updated second level of the waveformparameter to the second electrode. In the various embodiments, this caninclude changing the first level of the waveform parameter,automatically setting the second level of the waveform parameter basedon a ratio or other relationship between the first therapy range and thesecond therapy range, and delivering the electrical waveform to thefirst electrode and at the first level to the second electrode at thesecond level.

In some embodiments the computer-operable medium is programmed to changethe waveform parameter applied to the first electrode and automaticallyset the parameter for the waveform applied to the second electrode basedon a relationship between the first therapy range and the second therapyrange (e.g., a therapy range ratio or other scaling factor). Forexample, when a change command is received by the implantable device,the computer-operable medium can be programmed to (a) change thewaveform parameter applied to the first electrode by a first incrementand (b) set the waveform parameter applied to the second electrode by asecond increment in direct proportion to a therapy range ratio of thefirst therapy range to the second therapy range. In a different example,when a set of change commands is received, such as by the implantabledevice, the computer-operable medium is programmed to (a) change thewaveform parameter applied to the first electrode by a change incrementfor each change command received by the implantable device and (b) setthe waveform parameter applied to the second electrode according to abest-fit approximation of the therapy range ratio. In this latterexample the computer-operable medium can be programmed to set thewaveform parameter applied to the second electrode either by changingthe parameter applied to the second electrode by the same amount as thefirst electrode or by holding the parameter applied to the secondelectrode constant when the patient inputs a change command.

In some embodiments, the technology further includes determining and/orreceiving a scaling factor of the waveform parameter based on arelationship between the first and the second therapy ranges. Thecomputer-operable medium can be programmed to receive a predeterminedscaling factor of a waveform parameter based upon a relationship betweena first therapy range for the waveform parameter at a first area of thepatient and a second therapy range for the waveform parameter at asecond area of the patient. Alternatively, the computer-operable mediumcan automatically calculate the scaling factor based upon the first andsecond therapy ranges.

In some embodiments, the technology further includes delivering anelectrical waveform at a first level of the waveform parameter to thefirst electrode located at the first area of the patient and at a secondlevel of the waveform parameter to the second electrode, and deliveringan updated first level to the first electrode and delivering an updatedsecond level of the waveform parameter to the second electrode. In oneparticular example, the computer program is programmed to change thelevel of the waveform parameter applied to the first electrode implantedat the first area of the patient to an updated first level,automatically set the second level of the waveform parameter based on aratio or other relationship between the first therapy range and thesecond therapy range to an updated second level, and deliver theelectrical waveform at the updated first level to the first electrodeand at the updated second level to the second electrode.

In some embodiments, the computer-operable medium is programmed toprevent the waveform parameter applied to the first area from exceedinga first maximum and/or preventing the waveform parameter applied to thesecond area from exceeding a second maximum.

The waveform parameters for the foregoing technology can include theamplitude, impedance, voltage, pulse width, frequency, duty cycle andother parameters. For example, the waveform parameter can include thepower delivered via the first electrode and/or the second electrode overa given period of time.

Representative Systems and Methods

In the following discussion, FIGS. 1A-1B illustrate a representativeimplementation of a system 100 implanted in the spinal cord region of apatient 190, and FIGS. 2-7 illustrate representative components ofsystem, methods, routines, associated circuits, and/or waveforms formanaging pain across multiple areas of a patient. FIG. 1A schematicallyillustrates the treatment system 100 arranged relative to the generalanatomy of the patient's spinal cord 191 to provide relief from chronicpain and/or other conditions. The system 100 can include a waveformgenerator 101, which may be implanted subcutaneously within the patient190 and coupled to an electrode device 109 (e.g., a signal deliveryelement). In a representative example, the electrode device 109 includesa lead or lead body 110 that carries features or elements for deliveringtherapy to the patient 190 after implantation. The waveform generator101 can be connected directly to the lead body 110, or it can be coupledto the lead body 110 via a communication link 102 (e.g., an extension).As used herein, the terms lead and lead body include any of a number ofsuitable substrates and/or support members that carry devices forproviding therapy signals to the patient 190. For example, the lead body110 can include one or more electrodes or electrical contacts thatdirect electrical signals into the patient's tissue. In otherembodiments, the electrode device 109 can include devices other than alead body (e.g., a paddle) that also direct electrical signals and/orother types of signals to the patient 190.

The waveform generator 101 can transmit electrical signals (i.e.,waveforms) to the electrode device 109 that up-regulate (e.g., stimulateor excite) and/or down-regulate (e.g., block or suppress) target nerves.As used herein, and unless otherwise noted, the terms “stimulate” and“stimulation” refer generally to signals that have either type of effecton the target nerves, and the terms “electrical signals” and “electricalwaveforms” are used interchangeably. The waveform generator 101 caninclude a machine-readable medium (e.g., computer-operable medium orcomputer-readable medium) programmed or otherwise containinginstructions for generating and transmitting suitable therapy waveforms.The waveform generator 101 and/or other elements of the system 100 caninclude one or more processors 107, memories 108 and/or input/outputdevices. Accordingly, the process of managing pain across multiple areascan be performed by computer-executable instructions contained oncomputer-operable media, e.g., the processor(s) 107 and/or memory(s)108. The waveform generator 101 can include multiple portions, elements,and/or subsystems (e.g., for directing signals in accordance withmultiple signal delivery parameters) contained in a single housing, asshown in FIG. 1A, or contained in multiple housings. In any of theseembodiments, the waveform generator 101 and/or other implantedcomponents of the system 100 can include elements for detecting andresponding to patient movement, impedance changes or other variables.

In some embodiments, the waveform generator 101 receives power from anexternal power source 103. The external power source 103 can transmitpower to the implanted waveform generator 101 using electromagneticinduction (e.g., RF signals). For example, the external power source 103can include an external coil 104 that communicates with a correspondinginternal coil (not shown) within the implantable waveform generator 101.The external power source 103 can be portable and rechargeable for easeof use.

In another embodiment, the waveform generator 101 can receive power froman internal power source in addition to or in lieu of the external powersource 103. For example, the implanted waveform generator 101 caninclude a battery that is either non-rechargeable or rechargeable toprovide the power. When the internal power source includes arechargeable battery, the external power source 103 can be used torecharge the battery. The external power source 103 can in turn berecharged from a suitable power source (e.g., conventional wall power).

In some cases, an external programmer 105 (e.g., a trial stimulator) canbe coupled to the electrode device 109 during a trial procedure beforeimplanting the waveform generator 101. A practitioner (e.g., a physicianand/or a company representative) can use the external programmer 105 tovary the stimulation parameters provided to the electrode device 109 inreal time, and select optimal or particularly efficacious parameters.During the trial period, the practitioner can also vary the position ofthe electrode device 109. After the position of the electrode device 109and initial signal delivery parameters are established using theexternal programmer 105, the trial period continues for a limited timeperiod by providing the therapy to the patient 190 via signals generatedby the external programmer 105. In a representative application, thepatient 190 receives the trial therapy for one week. If the trialtherapy is effective or shows the promise of being effective, thepractitioner then replaces the external programmer 105 with theimplanted waveform generator 101. The practitioner can optionallyreplace or reposition the electrode device 109 at the same time. Thewaveform parameters are initially based on the experience of the trialperiod, but these parameters can be further adjusted remotely via awireless physician's programmer (e.g., a physician's remote) 111 and/ora wireless patient programmer 106 (e.g., a patient remote) at any time.Generally, the patient 190 has control over fewer parameters than thepractitioner. For example, the capability of the patient programmer 106may be limited to starting/stopping the waveform generator 101 andadjusting the stimulation amplitude applied to one or more areasadjacent the electrode device 109.

In any of the foregoing embodiments, the waveform parameters can bemodulated during portions of the therapy regimen across one or more ofthe areas adjacent the electrode device 109. For example, the frequency,amplitude, pulse width, duty cycle, and/or signal delivery location canbe modulated in accordance with a preset program, patient and/orphysician inputs, and/or in a random or pseudorandom manner. Suchparameter variations can be used to address a number of potentialclinical situations, including changes in the patient's perception ofpain, changes in the preferred target neural population, and/or patientaccommodation or habituation. In accordance with the present technology,one or more sets of areas adjacent to the signal delivery element 109are linked together for the purpose of modulating one or more of thewaveform parameters based on a scaling factor between the individualareas in each set. As explained in more detail below, the level of awaveform parameter applied to each area in a linked pair can bemodulated based upon a scaling factor between the corresponding areas.

FIG. 1B illustrates a representative lead 110 that can be connected tothe waveform generator 101. The lead 110 can have any suitable number ofcontacts C positioned along its length L for delivering electricaltherapy to the patient. For purposes of illustration, the lead 110 canhave 11 contacts C (identified individually as contacts C1, C2 . . .C11). In operation, one or more of the contacts C is cathodic andanother one or more of the contacts C is anodic. The contacts C can beindividually addressable so that any contact C or combination ofcontacts C can operate as a cathode, and any contact C or combination ofcontacts C can operate as an anode. The contacts C can be electricallygrouped in any of a wide variety of combinations, and individualcontacts C can perform different functions (e.g., cathodic functionsand/or anodic functions) at different times during the course of atherapy regimen. In any of these embodiments, each contact C may becoupled with a corresponding conductor 111 to the waveform generator101. The conductors 111 may have one or more connection points alongtheir lengths (e.g., at a junction with the waveform generator 101, andoptionally at a junction with an extension). Accordingly, the circuitfor a given pair of contacts C includes the contacts C, the patienttissue T between the contacts, the individual conductors 111, connectionpoints along the conductors 111, and connection points between theconductors 111 and the waveform generator 101.

FIG. 2 illustrates an overall process in accordance with a specificembodiment of the technology for managing pain in a patient using anelectrical waveform. In this embodiment, the patient has a first areawhich has a first therapy range for a waveform parameter and a secondarea which has a second therapy range for the waveform parameter. Themethod 200 can include changing the level of the waveform parameterapplied to a first electrode located at the first area of the patient(block 210), and automatically setting the level of the waveformparameter applied to a second electrode located at the second area ofthe patient (block 220). The level of the waveform parameter applied tothe second electrode is automatically set by the computer-operablemedium based on the magnitude of the change of the waveform parameterapplied to the first electrode and a relationship between the firsttherapy range and the second therapy range (block 220). The waveformparameter, for example, can be the amplitude, pulse width, duty cycle,frequency, power or other variable. The relationship between the firsttherapy range and the second therapy range can be a scaling factor thatcompensates for different sensation, therapy and pain thresholds betweenthe first and second areas. The method 200 accordingly links the levelof the waveform parameter applied to the second area of the patient tothe level of the waveform parameter applied to the first area of thepatient based on the relationship between the first and second therapyranges for the waveform parameter.

The method 200 is not limited to linking the adjustment of the level ofa single waveform parameter across different areas of the patient, butrather the method 200 can include linking changes in the levels of a setof parameters of the waveform applied to one area of the patient to thelevels of the same set of parameters of the waveform applied to anotherarea of the patient based on the scaling factor. The method 200 is alsonot limited to linking the adjustment for the level of just the firstand second areas of the patient, but rather the method 200 can includelinking the level of the waveform parameter to any number of areas ofthe patient's body in addition to, or in lieu of, linking the waveformparameter applied to the first and second electrodes located at thefirst and second areas of the patient. The use of “first” and “second”throughout is accordingly inclusive of additional like features, andthus unless otherwise expressly stated the use of “first” and “second”throughout does not exclude any additional like or similar features. Inseveral embodiments, the method 200 includes changing the level of thewaveform parameter applied to the first electrode and concurrentlysetting the level of the waveform parameter applied to the secondelectrode, but in other embodiments there can be a delay betweenchanging the level of the waveform parameter applied to the firstelectrode and setting the level of the waveform parameter applied to thesecond electrode.

The different areas of the patient can be sites relative to thepatient's spinal cord. For example, the first and second areas can belocated adjacent to the patient's spinal cord such that the electricalwaveform applied to the first area affects a first population of neuronswhile the waveform applied to the second area affects a secondpopulation of neurons. The first and second neuron populations can becompletely distinct from each other, or in other situations there can besome overlap among the different neuron populations.

The different areas of the patient are generally associated withdifferent areas of pain perceived by the patient. Referring to FIG. 1B,for example, any of the electrodes C1-C11 can be associated withindividual areas of the patient to apply energy to different populationsof neurons that control or are otherwise involved in the transmission ofpain signals associated with different regions of the patient. Themethod 200 can further include locating more than one electrode at eachindividual area of the patient. For example, electrodes C1-C4 can belocated at a first area A₁ of the patient, electrodes C5-C8 can belocated adjacent to a second area A₂ of the patient, electrode C9 can belocated adjacent to a third area A₃ of the patient, and electrode C10can be located at a fourth area A₄ of the patient. In other embodiments,only a single one of the electrodes C1-C11 can be located and/oractivated at a single area of the patient. The configuration of areasA₁-A₄ shown in FIG. 1B is merely one example, and a person skilled inthe art of implementing SCS systems will understand that the number ofareas and the number of electrodes per area varies and are not limitedto those shown in FIG. 1B.

The method 200 links the modulation of at least one waveform parameteracross two areas of the patient. For example, two or more of thedifferent areas of the patient A₁-A₄ can be linked together in one ormore sets in which a scaling factor is applied to changes of a waveformparameter between the different areas of a set. In one embodiment, areasA₁ and A₂ can be linked together to define a first area set in which ascaling factor S₁ is applied to the waveform parameter applied to eachof the areas A₁ and A₂. Similarly, the third area A₃ and the fourth areaA₄ can be linked together in a second area set in which a scaling factorS₂ is applied to the waveform parameter applied to the third and fourthareas A₃ and A₄ either in addition to, or in lieu of, applying thescaling factor S₁ to areas A₁ and A₂. FIG. 1B further illustrates thatthe second area A₂ and the third area A₃ can be linked together in athird area set to which a scaling factor S₃ is applied to the waveformparameter applied to areas A₂ and A₃. Any number of differentcombinations of areas and scaling factors may be implemented forcontrolling the waveform parameters among the different areas of one ormore area sets.

Several embodiments of the method 200 are particularly useful forcontrolling pain perceived in different regions of the back and/or lowerextremities (e.g., legs, buttocks, foot). Referring to U.S. PatentApplication No. 61/176,868, filed on May 8, 2009, now expired, which isincorporated herein by reference, the electrodes can be located adjacentto vertebral bodies T9-T12, and more specifically along vertebral bodiesT10-T11, for treating back and lower extremity pain. In otherembodiments, however, the electrodes can be located adjacent to othervertebral bodies for treating other types of pain or other conditions.

The scaling factor can be based on a relationship between the therapyranges of the waveform parameter for the individual areas of thepatient. The therapy range for a given area can be the range of thewaveform parameter that provides the desired pain control withoutinducing discomfort (e.g., sharp pain, adverse muscle effects, or otherunwanted effects). For example, the lower limit of a therapy range for agiven area can be based on the level of the waveform parameter at asensation threshold and/or a therapeutic threshold associated with theparticular area. The upper limit of the therapy range for the particulararea can be based on a level of the waveform parameter at a discomfortthreshold. The “sensation threshold” can be the level or range of thewaveform parameter at which the patient initially senses the electricalwaveform applied to the specific area. The “therapeutic threshold” canbe the level or range of the waveform parameter at which the patientexperiences a therapeutic effect, such as relieving pain, associatedwith the corresponding area. The sensation and therapeutic thresholdscan be the same or similar levels of the waveform parameter. The“discomfort threshold” can be the level or range of the waveformparameter that induces pain, unwanted muscle effects, or otherundesirable effects associated with the corresponding area. The lowerlimit of the therapy waveform may be set slightly above the sensationthreshold and/or the therapeutic threshold to provide a margin thatensures the patient receives the desired therapy. Conversely, the upperlimit of the therapy range can be less than the discomfort threshold toprovide a margin that ensures that the patient does not experiencediscomfort.

The method 200 can further include setting a maximum level for thewaveform parameter at each of the areas of the patient. For example, themethod 200 can further include setting a first maximum of the waveformparameter for the first area and setting a second maximum of thewaveform parameter for the second area. The first and second maximums ofthe waveform parameter can be less than the first and second discomfortthresholds, respectively. The method 200 can further include preventingthe first or second levels of the waveform parameter from exceeding thefirst or second maximums, respectively, so that the electrical waveformdoes not induce undesirable side effects in any of the linked areas.

The therapy ranges for the individual areas of the patient can bedetermined during the trial period and/or throughout the therapy afterfinal implantation. FIG. 3A is a flowchart illustrating an embodiment ofa routine for determining the therapy range of the waveform parameterassociated with an area of the patient. As described above, theelectrodes are implanted in the patient and the electrical waveforms aregenerated by a waveform generator to determine whether the electricalsignals provide a therapeutic effect for the specific patient. Theembodiment of the routine 300 illustrated in FIG. 3A includesdetermining a correlation between the electrodes and the areas of thepatient (block 310), delivering the electrical waveform to at least oneelectrode at a corresponding area of the patient (block 320), andmodulating a waveform parameter applied to the electrode (block 330).The correlation between the electrodes and the areas of the patient canbe determined by applying the electrical waveform to one or moreelectrodes either individually or in various combinations with eachother and recording the corresponding areas where the patient perceivesa sensation, a therapeutic effect, or discomfort. Based on themodulation of the waveform parameter, the method 300 further includesdetermining a level of the waveform parameter at which the patientperceives the application of the electrical waveform (block 340) withoutdiscomfort and determining a level of the waveform parameter at whichthe patient perceives an undesirable effect (block 350). The level ofthe waveform parameter at which the patient perceives the application ofthe electrical waveform (block 340) without discomfort can correspond tothe sensation threshold and/or the therapeutic threshold, and the levelof the waveform parameter at which the patient perceives an undesirableeffect (block 350) can correspond to the discomfort threshold. Asdescribed above, the lower and upper limits of the therapy range can bebased on these thresholds.

The therapy ranges can also be determined based on a patient usagehistory during the trial period and/or after final implantation of thepulse generator. FIG. 3B illustrates a routine 312 for determining thetherapy range in accordance with an embodiment of the technology. Inthis embodiment, the routine 312 includes applying an electricalwaveform to electrodes at different areas of the patient (block 322).The electrical waveform can be applied to one or more electrodes at theindividual areas of the patient to determine the therapy ranges for thecorresponding areas as explained above. The routine 312 further includesrecording the waveform parameter levels applied to the differentelectrodes at the different areas of the patient (block 332) over time.The usage history of the waveform parameter can be recorded in theonboard memory of the implantable device and then downloaded via awireless communication link to an external programmer during rechargingor at other times. The routine 312 further includes determining at leastone of the sensation threshold or the therapeutic threshold from theusage data (block 342) and determining the discomfort threshold from theusage data (block 352). The routine 312 can optionally includingdetermining the other of the sensation threshold or the therapeuticthreshold from the usage data (block 362) in addition to the thresholddetermined at block 362. The sensation threshold, discomfort thresholdand/or therapeutic threshold determined from the usage data can remainstatic throughout the therapy, or the routine can further includeupdating one or more of these thresholds on a continuous or periodicbasis (block 372).

The various thresholds at blocks 342, 352 and 362 can be determined byhaving the patient provide an input when the patient perceives asensation, a therapeutic effect or an undesirable effect associated withthe waveform. The patient inputs can be correlated with the levels ofthe waveform parameter to provide a series of data points fordetermining each of the sensation, therapeutic and/or discomfortthresholds. In a different embodiment, the thresholds can be based on anassessment of the patient's habits. For example, the lower limits of thetherapy range can be determined by identifying the lower range ofwaveform parameter levels consistently used by the patient because suchusage would indicate that the patient does not perceive the waveform ora therapeutic effect below such levels. The discomfort threshold may beassessed by ascertaining the levels of the waveform parameter at whichthe patient rapidly reduces the magnitude of the parameter and/or theupper range of waveform parameter levels used by the patient. A rapidreduction of the magnitude of the waveform parameter may be indicativeof an acute increase in pain or other undesirable effects, whereas theupper range would indicate the patient perceives discomfort above suchlevels. The therapeutic threshold also may be determined by identifyingthe levels at which the waveform parameters are maintained for extendedperiods of time because this would indicate that the electrical waveformis providing the desired therapeutic effect for controlling or otherwisemanaging the patient's pain.

The actual linked modulation based on the relationships between thetherapy ranges can be executed in a number of different ways. Forexample, one embodiment of the method 200 changes the level of thewaveform parameter applied to the first area by a first increment andautomatically changes the level of the waveform parameter applied to thesecond area by a second increment in direct proportion to the ratio ofthe first therapy range to the second therapy range. The ratio of thefirst therapy range to the second therapy range can be less than 1:1,equal to 1:1, or greater than 1:1 depending upon the sizes of theindividual ranges. The ratio can have a positive value when the waveformparameter levels in different areas are positively correlated, and anegative value when the waveform parameter levels are negativelycorrelated. A negative correlation can exist, for example, when thepatient experiences a stronger than desired stimulation in one area, anda weaker than desired stimulation in another area. In such instances,the scale factor can include the ratio described above, optionallymodified by patient input.

When the amplitude is the waveform parameter being modulated, the ratioof the first therapy range for the first area of the patient to thesecond therapy range for the second area of the patient can be definedby the equation:

${Ratio} = \frac{A_{1\; P} - A_{1\; T}}{A_{2\; P} - A_{2\; T}}$

In this equation, A_(1P) is the amplitude at which the patientexperiences pain at the first area, A_(1T) is the amplitude at which thepatient experiences a therapeutic effect at the first area, A_(2P) isthe amplitude at which the patient experiences pain at the second area,and A_(2T) is the amplitude at which the patient experiences atherapeutic effect at the second area. In this embodiment, the change inthe level of the waveform parameter applied to the second area is theproduct of the magnitude of the first increment that the waveformparameter was changed at the first area and the ratio of the firsttherapy range to the second therapy range.

FIG. 4 illustrates in a specific example of setting the waveformparameter applied to the second electrode in direct proportion to thetherapy range ratio. The example shown in FIG. 4 is for purposes ofillustration and is not limiting in any way. In this example, if thefirst area of the patient has a pain threshold (A_(1P)) of 6 mA and atherapy threshold (A_(1T)) of 3 mA, and if the second area of thepatient has a pain threshold (A_(2P)) of 7 mA and a therapy threshold(A_(2T)) of 5 mA, then the first therapy range is 3 mA and the secondtherapy range is 2 mA. This results in a therapy range ratio of 3:2based on the equation above. As a result, for every first increment thatthe waveform parameter is changed at the first area A₁, the secondincrement that the waveform parameter is changed at the second area A₂is two-thirds of the first increment. If the therapy range ratio of thefirst therapy range to the second therapy range is 2:1, then the secondincrement is 50% of the first increment.

FIG. 5 illustrates another example of implementing an embodiment of themethod 200 in which the levels of the waveform parameter are modulatedto achieve a best-fit approximation of the relationship between thefirst and second therapy ranges. In this embodiment, each time thewaveform parameter applied to the first electrode is changed by anincremental amount, the waveform parameter applied to the secondelectrode is set by either (a) changing the waveform parameter appliedto the second area by the same incremental amount or (b) holding thewaveform parameter applied to the second area constant. For example,when the therapy range ratio of the first therapy range to the secondtherapy range is 3:2 as described above, then the level of the waveformparameter applied to the second electrode is changed by two of theincremental amounts for every three incremental amounts that the levelof the waveform parameter is changed at the first electrode. Stateddifferently, each time the patient pushes a button to increase ordecrease the waveform parameter, the waveform parameter for the firstelectrode is changed by a full increment, but the waveform parameter ischanged at the second area only every two out of three times that thepatient pushes the button. FIG. 5 illustrates this point for the exampleof a therapy ratio of 3:2 at times t₁, t₂ and t₃. More specifically,when the patient pushes a button or otherwise inputs a change commandusing the patient programming at time t₁, the level of the parameter isincreased by a first increment 1.0 at both the first area A₁ and thesecond area A₂. This provides the best fit for a 3:2 therapy ratiobecause the direct proportional increase at the second area A₂ would beapproximately 0.67 such that applying an incremental change of 1.0 toarea A₂ is closer to the therapy ratio than holding the value constant.At time t₂, the patient inputs another command to increase the waveformparameter by another full increment at area A₁ to 2.0, but the value ofthe waveform parameter applied to area A₂ is held constant. This isbecause after two increases of the incremental value applied to area A₁,the direct proportional value of the waveform parameter for area A₂would be 1.33 such that holding the waveform parameter applied to thesecond area constant at 1.0 provides a better fit than increasing thewaveform parameter applied to the second electrode to 2.0. At time t₃,the patient enters another input to change the waveform parameters suchthat the level of the waveform parameter associated with the first areaA₁ is increased to 3.0 and the level of the waveform parameterassociated with the second area A₂ is increased to 2.0. The foregoingexamples using the ratio of 3:2 are merely for illustration, and it willbe appreciated that the actual ratio of the first therapy range to thesecond therapy range can be any ratio depending upon the values for thefirst and second therapy ranges.

The method 200 can further include preventing a waveform parameterapplied to the first area from exceeding a first maximum and preventingthe waveform parameter applied to the second area from exceeding asecond maximum. Because each area of the patient may have a differentmaximum for the waveform parameter, the method 200 can includedetermining a first maximum for the waveform parameter associated withthe first area and determining a second maximum for the waveformparameter associated with the second area above which application of thewaveform causes discomfort at either or both of the areas. By preventingthe waveform parameter from exceeding one or both of the first and/orsecond maximums, the patient will not exceed the pain threshold of onearea while trying to increase the amplitude applied to another area.

FIG. 6 is a flowchart illustrating a method 600 in accordance withanother embodiment of the technology. In this embodiment, the method 600includes delivering an electrical waveform at a first level of thewaveform parameter to a first electrode at the first area and at asecond level of the waveform parameter to a second electrode at thesecond area (block 610). The method 600 further includes changing thefirst level of the parameter (block 620) and setting the second level ofthe parameter based on a ratio of the first therapy range to the secondtherapy range (block 630). The electrical waveform is then delivered atthe first level of the parameter to the first electrode and at thesecond level of the parameter to the second electrode (block 640).

FIG. 7 illustrates a method 700 in accordance with yet anotherembodiment of the technology. In this embodiment, the method 700includes selecting at least two areas for linked modulation of thewaveform parameter including a first area having a first therapy rangefor the waveform parameter and a second area having a second therapyrange for the waveform parameter (block 710). The method 700 furtherincludes determining a scaling factor of the waveform parameter based ona relationship between the first and second therapy ranges (block 720).The method 700 continues by delivering an electrical waveform at a firstlevel of the waveform parameter to a first electrode located at thefirst area and at a second level of the waveform parameter to a secondelectrode located at the second area (block 730). The method 700 furtherincludes changing the first level of the waveform parameter to anupdated first level (block 740) and setting the second level of thewaveform parameter to an updated second level based on the scalingfactor and the magnitude of the change of the first level of thewaveform parameter (block 750). The electrical waveform is thendelivered at the updated first level of the waveform parameter to thefirst electrode and at the updated second level of the waveformparameter to the second electrode (block 760).

In any of the foregoing embodiments, the computer-operable medium of thesystem 100 can be programmed to execute any or all of the embodiments ofthe methods described above. Additionally, the system 100 can furthercomprise a memory containing a history of patient usage patterns of thewaveform applied to the first and second electrodes, and thecomputer-operable medium can be programmed to determining whether thefirst area of the patient is linked to the second area of the patient.In still additional embodiments, the computer-operable medium can beprogrammed to determine whether the first area of the patient is notlinked to the second area of the patient, and in such circumstances tochange the first waveform parameter applied to the first electrode andset the second waveform parameter applied to the second electrodeindependently of each other.

Any of the foregoing methods and systems can include further embodimentsfor adapting the linked modulation of the waveform parameter to theposition of the patient. For example, the system 100 can furthercomprise a memory including a first ratio of the first therapy range tothe second therapy range associated with a first patient position and asecond ratio of the first therapy range to the second therapy rangeassociated with a second patient position. The system can furthercomprise a position detector, and the computer-operable medium can beprogrammed to change the waveform parameter applied to the firstelectrode and set the waveform parameter applied to the second electrodebased on (a) the first ratio when the position detector indicates thatthe patient is in the first patient position or (b) the second ratiowhen the position detector indicates that the patient is in the secondpatient position. The position detector can comprise an accelerometer,or the position detector can comprise an impedance detector.

Several embodiments of the systems, methods and routines of thetechnology described above can simplify and enhance the ability tochange a waveform parameter across several areas of the patient. Forexample, the patient can merely increase or decrease the intensity ofthe waveform parameter and the systems and methods automatically adjustthe waveform parameter across the different areas without being limitedby the area with the lowest pain threshold or the highest therapeuticthreshold. As explained above, existing linked mode systems that do notprovide scaling between the various areas are limited to increasing theintensity of the waveform parameter so that it does not exceed the painthreshold level of the area having the lowest pain threshold. Manyembodiments of the present technology avoid or mitigate such alimitation because the scaling factor allows the intensity of theparameter to be increased differently across the areas depending on thedifferent pain thresholds. This enables some areas to receive moreintense stimulation that would otherwise cause pain in areas with lowerpain thresholds. Several embodiments of the technology also maintain therelative levels of the waveform parameter over a long period of time toprovide more consistent results. Existing linked mode systems change theintensity of the waveform parameter at different areas by equalincrements for each change command and merely prevent the waveformparameter from exceeding an upper limit at each area, but these systemsthen allow the waveform parameter to be decreased from their maximums byequal increments when the patient inputs the change commands. Severalembodiments of the technology avoid or mitigate this problem because thescaling factor enables the waveform parameter to be changed by differentamounts at different areas. Therefore, several embodiments of thetechnology simplify the ongoing modulation of waveform parameters andenhance the efficacy of managing pain.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A system for managing pain in a patient using an electrical waveform,comprising: an electrode device configured to be implanted into apatient and including a plurality of electrodes having at least a firstelectrode associated with a first area of the patient and a secondelectrode associated with a second area of the patient, wherein thefirst area has a first therapy range for a waveform parameter and thesecond area has a second therapy range for the waveform parameter; andan implantable device configured to be coupled to the electrode device,the implantable device including a power supply, a waveform generatorconfigured to generate the waveform, and a computer-operable mediumoperatively coupled to the waveform generator, the computer-operablemedium being programmed to change the waveform parameter applied to thefirst electrode and automatically set the waveform parameter applied tothe second electrode based on a relationship between the first therapyrange and the second therapy range. 2-45. (canceled)